Welding Cast Iron With Stainless Steel. In my area it is called Ni-rod. Doing so successfully will depend on the kind of iron being welded as.
Cast iron typically has a carbon content of 2 - 4 roughly 10 times as much as most steels. It does not expand and contract significantly during the heating and cooling of the fusion process and poses a challenge to use it. Metal inert gas GMAW or MIG processes can get excellent cast iron welds.
First usually you are doing a repair job or a retrofit if you are asking about welding cast iron to steel so be sure to check the parts thoroughly to ensure there are no stress cracks or other signs of damage.
Replacing a part of cast iron can cost thousands or hundreds of dollars. There are basically two types of filler metals that are used with cast iron. There are some real good rods now for cast iron. Because high amount of chromium in filler and high amount of carbon in cast iron combine together to make some carbon reached chromium carbide which is brittle.